1. Field of the Invention
The present invention is directed to a switched reluctance motor and more specifically, to a switched reluctance motor having a rotor with vibration absorbing means.
2. Description of the Prior Art
A conventional switched reluctance motor is disclosed in, for example, GB 2 231 214A. This switched reluctance motor includes a housing, a stator fixed in an inner bore of the housing and formed by laminating electromagnetic steel plates and a rotor disposed in the stator and formed by laminating electromagnetic steel plates. The rotor is fixed to an output shaft which is rotatably supported on side portions of the housing through bearings and thereby is rotatably disposed in the stator. The rotor has a plurality of pairs of rotor pole portions which project outward in the diametrical direction and which extend in the axial direction. The stator has a plurality of pairs of opposing stator pole portions which project inward in the diametrical direction and which extend in the axial direction. Each of the stator pole portions is opposed to each of the rotor pole portions in response to the rotation of the rotor and a certain clearance is maintained between the stator pole portions and the rotor pole portions which are opposed to each other. A coil is wound on each of the stator pole portions. The coils, which are wound on each of the pairs of opposing stator pole portions, are connected in series with each other whereby a magnetic flux is generated between each pair of stator pole portions when current is supplied to the coils which are wound thereon. A magnetic attracting force results between the rotor pole portions and the stator pole portions which are approaching each other. This magnetic attracting force is changed by controlling supply current by means of switching elements in response to the rotational position of the rotor whereby rotary torque is produced.
The current which is supplied to the coil wound on one pair or several pairs of stator pole portions being approached by one pair or several pairs of rotor pole portions is switched on and off such as a pulse. In general, the current is switched on when a pair of rotor pole portions begins to be aligned with a pair of stator pole portions, and the current is switched off before a pair of rotor pole portions is aligned with a pair of stator pole portions. Thus, the magnetic attracting force increases proportionally while the current is supplied, and disappears in a moment when the current is switched off. On one hand, rotary torque is obtained by this magnetic attracting force. On the other hand, a pair or several pairs of stator pole portions are attracted radially to a pair of rotor pole portions by this magnetic attracting force, respectively, so that a load is radially applied to the rotor.
The bearings, which support the rotor on the side portions of the housing, normally allow a certain relative movement or play in the radial direction. Furthermore, due to a measuring error in making the stator and the rotor, the magnetic attracting force generated between the rotor pole portions and the stator pole portions which are approaching each other is unsymmetrical. As a result, the rotor is attracted radially to the stator pole portion which generates a large magnetic attracting force. When the magnetic attracting force disappears, this radial load acting on the rotor disappears suddenly and simultaneously the bearings supporting the rotor receive an impulse. This impulse to the bearings is generated periodically in response to the rotation of the rotor whereby vibration of the side portions of the housing generates objectionable acoustic noise.